1. Field of the Invention
The present invention relates to a semiconductor device including thin film transistors.
2. Description of the Related Art
Different characteristics are required for thin film transistors that are used in semiconductor devices, depending on the purpose and function of the semiconductor devices. In order to satisfy the requirements, it is important to control characteristics of thin film transistors, and a technique of manufacturing thin film transistors having characteristics suited for their purposes has been researched (for example, Reference 1: Japanese Published Patent Application No. 19-27624).
In Reference 1, a thin film transistor including an impurity region with an LDD (lightly doped drain) structure is formed using a sidewall, and leak current when the thin film transistor is in an OFF state is reduced.